Of all England’s medieval monarchs, William the Conqueror is the most unfairly maligned. Here was a duke of Normandy who mounted a successful seaborne invasion of the much larger and more powerful kingdom of England, who triumphed in one of the most desperate battles ever fought, and who held on to his prize doggedly despite repeated attempts to unseat him. Even contemporary Englishmen, whatever their other complaints, conceded that he had brought peace and security to the country.

Yet for many English people today, all this counts for nothing, because William was a foreigner; in the popular understanding, the Anglo-Saxons are ‘us’ and the Normans are ‘them’. Stir in the hoary old misapprehension that history is always written by the victors and you can discredit anything positive that contemporaries ever said about William. Judge him by the moral standards of our time rather than his own and you can convict him on any number of counts: brutality, war crimes, genocide. Every couple of years a little book appears on either William or the Norman Conquest and does just that.

Mark Hagger’s new biography of the Conqueror, thankfully, does not. The author is a genuine expert in the field, and has no truck with those who try to condemn his subject out of context. Thus William’s decision to maim the men who mocked him at Alençon is shown to be normal behaviour for an 11th-century warlord; contemporaries saw nothing unusual in it.

More daringly, Hagger applies the same argument to William’s devastation of northern England during the winter of 1069–70, the so-called Harrying of the North, arguing that “his methods were entirely in keeping with the way that war was waged in his time”.

If Hagger perhaps goes too far here – the methods may have been unexceptional, but the death-toll was surely not – in general, his judgements are sensible and sound. Although one could quibble here and there on a particular point, his interpretation of events is convincing and his arguments academically up-to-the-minute.

Where the book falls down is in its uneven coverage and curious omissions. Large sections are given over to discussions of the diplomatic, for example, or what William might have worn; but there is no mention of his pioneering chivalry, or his opposition to slavery, or his crucial visit to England in 1051. There are asides on the ordeals and curses employed by the medieval church, but no introduction to the history of Normandy or northern France to help place the Conqueror in context. The king’s relationship with his family is summarised in less than a page; Harold Hardrada is mentioned only in brackets.

This is a pity, as one would have liked to have heard more on these topics from an author so clearly well qualified to guide us.